1. Field of the Invention
The present invention relates generally to a slat conveyor chain for conveying articles while a treatment liquid such as soap-and-water solution is supplied onto the load-bearing upper surface of the slat conveyor chain. More particularly, this invention relates to such a slat conveyor chain which is particularly suitable for conveyance of PET (polyethylene terephthalate) bottles, cans or the like containers for medicines and beverages.
2. Description of the Related Art
Conventionally, a slat conveyor chain formed from synthetic resin is used for conveyance of PET bottles, cans or the like containers for medicines and beverages.
As shown in FIGS. 8A and 8B, the conventional synthetic resin slat conveyor chain includes a series of slats 1 and chain links 2 formed integrally with respective undersides of the slats 1 and articulated by pins 3 at their reinforcement ribs to form an endless chain. The slats 1 are made from an engineering plastics such as polyacetal resin. The pins 3 are formed from stainless steel or engineering plastics.
When used in various production lines, the conventional slot conveyor chain is looped around a pair of horizontally spaced drive and driven sprockets S1, S2 and is driven by the drive sprocket 1 to transport articles W such as beverage containers carried on respective load-bearing upper surfaces of the slats 1 while respective undersides of the slats 1 are stably guided by a pair of laterally spaced guide rails R, R (FIG. 9) located on opposite sides of the links 3.
To protect the beverage containers W against an abrasive mark or scar during conveyance on the load-bearing upper surfaces of the slats 1, and to secure stable conveyance of the containers W with minimum abrasive wear of the chain, a soap-and-water solution is showered from a nozzle N onto the load-bearing upper surfaces of the slats 1 to lower the friction coefficient of the load-bearing upper surfaces and to lubricate the chain. The nozzle N is disposed above the slat conveyor chain at a position near the driven sprocket S2, as shown in FIG. 10.
The PET bottles, for which demand has increased in recent years, are relatively soft. Accordingly, when many such relatively soft PET bottles are accumulated on the synthetic resin slat conveyor chain during conveyance, the accumulated PET bottles are likely to deformed or otherwise damaged due to a large line pressure (conveyance resistance) resulting from an increased frictional resistance produced between the load-bearing upper surfaces of the slats 1 and bottom surfaces of the PET bottles.
Especially for those PET bottles having a bottom wall of petaloid shape, stable conveyance is almost impossible because the PET bottles are likely to come down or fall during conveyance due to their very unstable petaloid-shaped bottom walls. To deal with this problem, the amount of soap-and-water solution showered onto to the load-bearing upper surfaces of the slats is increased to a level greater than as used for conveyance of beverage cans. However, due to the increased supply of soap-and-water solution, the slat conveyor chain becomes excessively wet and the soap-and-water solution stays on part of the slat conveyor without draining. Excessive soap-and-water solution, which may stay on the load-bearing upper surfaces of the slats or between the undersides of the slats and the guide rails, scatters around a conveyor frame and thus causes contamination of working environment around the conveyor frame. Additionally, the scattered soap-and-water solution may cause corrosion of bearings fitted around drive and drive shafts of a chain drive mechanism and corrosion of a speed reducer of the chain drive unit, resulting in considerable shortening of the service life of the chain drive mechanism. These problems also occur when the articles to be conveyed are bins or when vast amounts of washing liquid are used for washing articles while being conveyed.